I finally seem to have nailed down the cause of the Invalid Seek Offset errors. It's a large vfp6/SP3 app, running under NT4.6a only (no trouble with Win9x). This after reading many MSDN docs and observing the NT Performance screen, and then reproducing the problem with the network cable pulled out of the machine.

I'm fairly sure it's the local NT File Caching. According to docs, it is allocated in 4MB chunks, called "offsetting" sometimes. My app loads at just under 4, but can easily exceed 4 after opening up more modules & forms, so it opens a 2nd file-caching block. Then when the vfp app returns to a table originally opened in the first block, NT can't find the address, it's looking in the second block, the wrong place.

Does this make sense, and if so, any ideas on what I need to alter on NT to eliminate or change the 4MB "blocking"?